Compound semiconductor device including diffusion preventing layer to suppress current collapse phenomenon, method of manufacturing compound semiconductor device, power supply unit, and amplifier

Abstract

A compound semiconductor device disclosed herein includes a substrate, an electron transit layer formed on the substrate, a compound semiconductor layer containing gallium and formed on the electron transit layer, a diffusion preventing layer containing gallium oxide and formed on the compound semiconductor layer, an insulation layer formed on the diffusion preventing layer, and a source electrode, a drain electrode, and a gate electrode formed over the electron transit layer at a distance from one another.

What is claimed is: 
     
       1. A compound semiconductor device comprising:
 a substrate; 
 an electron transit layer formed on the substrate; 
 a compound semiconductor layer containing gallium and formed on the electron transit layer; 
 a diffusion preventing layer containing gallium oxide and formed on the compound semiconductor layer; 
 an insulation layer formed on the diffusion preventing layer; 
 a source electrode, a drain electrode, and a gate electrode formed over the electron transit layer at a distance from one another; and 
 a barrier layer formed on the electron transit layer, 
 wherein the compound semiconductor layer is a cap layer of gallium nitride formed on the barrier layer, and 
 the cap layer includes:
 an upper layer located close to the diffusion preventing layer; and 
 a lower layer located below the upper layer, 
 
 wherein a composition ratio of gallium in the upper layer is smaller than a composition ratio of gallium in the lower layer. 
 
     
     
       2. A power supply unit comprising:
 the compound semiconductor device according to  claim 1 . 
 
     
     
       3. An amplifier comprising:
 the compound semiconductor device according to  claim 1 . 
 
     
     
       4. A compound semiconductor device comprising:
 a substrate; 
 an electron transit layer formed on the substrate; 
 a compound semiconductor layer containing gallium and formed on the electron transit layer; 
 a diffusion preventing layer containing gallium oxide and formed on the compound semiconductor layer; 
 an insulation layer formed on the diffusion preventing layer; and 
 a source electrode, a drain electrode, and a gate electrode formed over the electron transit layer at a distance from one another, 
 wherein the compound semiconductor layer is a barrier layer formed on the electron transit layer, 
 the barrier layer contains III group element other than the gallium, 
 the diffusion preventing layer contains an oxide of the III group element other than the gallium oxide, and 
 the barrier layer includes:
 an upper layer located close to the diffusion preventing layer; and 
 a lower layer located below the upper layer, 
 
 wherein a composition ratio of the III group element in the upper layer is smaller than a composition ratio of the III group element in the lower layer. 
 
     
     
       5. The compound semiconductor device according to  claim 4 , wherein the III group element is aluminum, and
 the barrier layer is an aluminum gallium nitride layer. 
 
     
     
       6. The compound semiconductor device according to  claim 4 , wherein the III group element includes aluminum and indium, and
 the barrier layer is an aluminum gallium nitride layer to which indium is added. 
 
     
     
       7. A power supply unit comprising:
 the compound semiconductor device according to  claim 4 . 
 
     
     
       8. An amplifier comprising:
 the compound semiconductor device according to  claim 4 . 
 
     
     
       9. A method of manufacturing a compound semiconductor device, the method comprising:
 forming an electron transit layer on a substrate; 
 forming a compound semiconductor layer containing gallium on the electron transit layer; 
 forming a diffusion preventing layer containing gallium oxide on the compound semiconductor layer; 
 forming an insulation layer on the diffusion preventing layer; 
 forming a source electrode, a drain electrode, and a gate electrode over the electron transit layer at a distance from one another; and 
 forming a barrier layer on the electron transit layer, 
 wherein the compound semiconductor layer is a cap layer of gallium nitride formed on the barrier layer, and 
 the cap layer includes:
 an upper layer located close to the diffusion preventing layer; and 
 a lower layer located below the upper layer, 
 
 wherein a composition ratio of gallium in the upper layer is smaller than a composition ratio of gallium in the lower layer. 
 
     
     
       10. The method of manufacturing a compound semiconductor device according to  claim 9 , wherein
 the forming of the diffusion preventing layer is performed by oxidizing the compound semiconductor layer. 
 
     
     
       11. A method of manufacturing a compound semiconductor device, the method comprising:
 forming an electron transit layer on a substrate; 
 forming a compound semiconductor layer containing gallium on the electron transit layer; 
 forming a diffusion preventing layer containing gallium oxide on the compound semiconductor layer; 
 forming an insulation layer on the diffusion preventing layer; and 
 forming a source electrode, a drain electrode, and a gate electrode over the electron transit layer at a distance from one another, 
 wherein the compound semiconductor layer is a barrier layer formed on the electron transit layer, 
 the barrier layer contains III group element other than the gallium, 
 the diffusion preventing layer contains an oxide of the III group element other than the gallium oxide, and 
 the barrier layer includes:
 an upper layer located close to the diffusion preventing layer; and 
 a lower layer located below the upper layer, 
 
 wherein a composition ratio of the III group element in the upper layer is smaller than a composition ratio of the III group element in the lower layer.